This invention relates to tissue welding techniques and apparatus for accomplishing tissue welding and, more particularly, to a method and an apparatus by which tissue may be reliably welded under controlled conditions.
Lasers of various types have long been used in various medical applications. In a wide variety of surgical techniques, a beam of laser light is used to cut tissue, and to coagulate along the cut at the same time. Although commonly used for tissue destruction, lasers have not gained the same widespread use for reconstructive procedures. Some progress has previously been made, however, in the use of laser energy for joining tissue, commonly termed tissue welding. The ultimate goal is to facilitate the joining of two tissues with a minimum of scar and good tensile strength of the apposed edges.
The mechanism of tissue welding is complex, and there are many variables that can be adjusted or modified in the welding process. Some evidence suggests that the mechanism of welding may vary depending upon which type of laser is used. Welding of blood vessels with an Nd:YAG laser produces an interdigitation of collagen which is the structural basis of the effect. As such, the collagen fibrils develop a change in periodicity but are still recognizable. Similarly, welding with an argon laser likely involves a structural change in the welded tissues.
In contrast to the argon and Nd:YAG lasers, which penetrate through the tissue, the CO.sub.2 laser produces heating with only superficial penetration. As a consequence, the CO.sub.2 laser probably accomplishes welding through yet another mechanism. A CO.sub.2 laser produces heating at the tissue surface, and this destroys tissue to the extent that a coagulum is produced which seals the edges to be joined. This denaturation of proteins occurs between 60.degree. C. and 70.degree. C.
The success of tissue union is dependent on several factors. First, it is necessary to align the edges of the tissue without tension. Second, a close approximate in the shape of the tissue edges is essential so that the laser energy is equally distributed to both edges. Third, since laser welding will inevitably destroy some of the tissue edge, it is important to have enough tissue so that stricture will not occur. Fourth, an adjustment of laser parameters to minimize peripheral tissue destruction will improve results. A protein solder has also been found to be helpful in minimizing the last two problems, as seen in several reports. Poppas, D., Schlossberg, S., Richmond, I., et al: "LASER WELDING IN URETHRAL SURGERY: IMPROVED RESULTS WITH A PROTEIN SOLDER" The Journal of Urology, Vol. 139, February 1988, pages 415-417; and Ganesan, G., Poppas, D., Devine, C.: "URETHRAL RECONSTRUCTION USING THE CARBON DIOXIDE LASER: AN EXPERIMENTAL EVALUATION" The Journal of Urology, Vol. 142, October 1989, pages 1139-1141.
In the past, the success of the tissue welding process has clearly been dependent in part upon the skill of the surgeon operating the laser. When lasers are used clinically for destructive purposes, the effect of laser light on the tissue is determined principally by visual observation. Since tissue destruction is the goal, assessing the degree of destruction by visual inspection is a fairly straightforward process. This is especially true of the CO.sub.2 laser which has a very short extinction coefficient. When using the Nd:YAG laser, some guidelines are available to help assess the amount of laser energy needed. Since the Nd:YAG laser has a longer extinction coefficient, however, tissue changes at the surface may not always be indicative of the effects that the laser energy has produced deeper in the tissues.
Determining when the end point of the tissue fusion process has been reached merely based on visual observation of the irradiated tissue, as has been done in the past, is less acceptable than using visual observation with destructive procedures. In prior tissue welding techniques, the surgeon has typically observed the tissue as it was irradiated, and when the tissue has changed to a golden brown color, welding is stopped. It will be appreciated, therefore, that the success rate achieved in laser welding techniques has been operator dependent to a significant degree.
It is seen, therefore, that there is a need for an improved method of tissue welding, and for apparatus for effecting this method, in which tissues are joined in an atraumatic, rapid, and reliable fashion.